This specification relates generally to information retrieval, particularly to modifying access controls in a search index.
Search engines identify resources (e.g., images, audio, video, Web pages, text, documents) that are relevant to a user's needs and present information about the resources in a manner that is useful to the user. A search engine may be used to conduct a search of a source of data, e.g., the Internet, a social network, a local data source, non-networked content, or the like. Typically, a search engine receives a search query from a user, consults an appropriate search index to identify subject matter relevant to the search query, obtains snippets of the relevant subject matter, ranks the snippets, and output the snippets for presentation in a Web browser.